Based on work from Noor Ahsan, we merge the important part of do_stage
into do_install and then set NATIVE_INSTALL_WORKS. We also add a function
for getting the gdb version for packaging up gdbserver and ship that.

* Later versions of u-boot sometimes have top level make targets
such as u-boot.imx, u-boot.kwb, and for upcoming TI devices
u-boot.ti.
* These targets define different calls to the mkimage tool to
change the images created, such as changing the load address.
* This change allows recipes to change the default make target
of "all" to something like u-boot.ti or u-boot.imx by setting
the UBOOT_MAKE_TARGET variable.